Spin-boson coupling in continuous-time quantum Monte Carlo

A vector bosonic field coupled to the electronic spin is treated by means of the continuous-time quantum Monte Carlo method. In the Bose Kondo model with a sub-Ohmic density of states $ρ_{B}(ω) \propto ω^{s}$ with s=0.2, two contributions to the spin susceptibility, the Curie term T^{-1} and the term T^{-s} due to bosonic fluctuations, are observed separately. This result indicates the existence of a residual moment and a hidden critical behavior. By including hybridization with itinerant electrons, a quantum critical point is identified between this local-moment state and the Kondo singlet state. It is demonstrated that the energy scale of the bosonic fluctuations is not affected by the quantum phase transition.

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